Each browser handles the individual file cache differently, 300MB is way too big to consider. I would bring the maximum file size to 80MB, or 50MB may be better. It’s not just an upper limit, there are other conditions. You may be able to improve the age by sever/content type configuration but I wouldn’t worry too much about this.
You will make better use of browser cache and asynchronous loading of assets, if you separate the assets into multiple files. You can use AssetManager and AssetContainer to your advantage.